Dynamic bond-driven bio-based polyurethane-modified asphalt: Preparation, performance evaluation, and self-healing behavior

Thermosetting polymer-modified asphalt exhibits excellent high-temperature stability and mechanical performance, but its non-renewable raw materials and poor reparability and recyclability conflict with sustainable green pavement development. Therefore, based on the renewability of castor oil and the dynamic reversibility of disulfide bonds, a thermosetting bio-based self-healing polyurethane-modified asphalt (TBSPUA) was designed and prepared. The results showed that the modifier containing 20 % castor oil (TBSPU-20 %) achieved an optimal balance between mechanical performance and self-healing ability, making it suitable for asphalt modification, and TBSPUA samples with different dosages were prepared using TBSPU-20 % as the modifier. When the TBSPU content exceeded 50 wt%, phase inversion occurred, and the system transitioned from asphalt-dominated to polymer-network-dominated. At 55 wt% modifier content, TBSPUA reached a tensile strength of 3.61 MPa and an elongation at break of 134.3 %, achieving the best balance between strength and toughness. The fracture–healing–fracture test and fluorescence microscopy confirmed that TBSPUA achieved efficient self-healing under hot-pressing conditions, with a maximum healing efficiency of 69.81 %. The synergistic effects of disulfide and hydrogen bonds significantly improved interfacial healing and structural integrity. Fatigue-healing results showed that the healing index(HI) first increased and then decreased with dosage at 90 °C, with TBSPUA-55 wt% exhibiting the highest HI of 91.23 %, demonstrating excellent self-healing performance and dynamic stress relaxation capability.